feat: add System Health monitoring mode

Real-time dashboard for host metrics (CPU, memory, disk, temperatures),
active decoder process status, and SDR device enumeration via SSE streaming.
Auto-connects when entering the mode with graceful psutil fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

routes/__init__.py

@@ -30,6 +30,7 @@ def register_blueprints(app):
     from .sstv import sstv_bp
     from .sstv_general import sstv_general_bp
     from .subghz import subghz_bp
+    from .system import system_bp
     from .tscm import init_tscm_state, tscm_bp
     from .updater import updater_bp
     from .vdl2 import vdl2_bp
@@ -75,6 +76,7 @@ def register_blueprints(app):
     app.register_blueprint(signalid_bp)  # External signal ID enrichment
     app.register_blueprint(wefax_bp)  # WeFax HF weather fax decoder
     app.register_blueprint(morse_bp)  # CW/Morse code decoder
+    app.register_blueprint(system_bp)  # System health monitoring
 
     # Initialize TSCM state with queue and lock from app
     import app as app_module